This invention relates to improvements in steering column assemblies of the kind including a support bracket that permits collapse during a crash. It also relates to steering assemblies including a support bracket.
Steering column assemblies for automotive vehicles and the like are increasingly required to be adjustable for steering wheel distance known as reach. This requires the column shroud, within which the steering column shaft attached to the steering wheel is rotatably located, to be fixed to the vehicle by a clamp mechanism which can be locked and unlocked to either prevent or permit adjustment of the column shroud position respectively.
One common arrangement uses a telescopic column shroud which comprises an inner member and an outer member—typically two elongate metal tubes—which slide one inside the other to permit reach adjustment. Fixing rails are provided on one of the tubes and are secured to a first support bracket by a releasable clamp mechanism. The first support bracket is in turn secured to an immobile part of the vehicle chassis, often by securing a-second support bracket to the first support bracket, or to frangible capsules supported by the first support bracket that is, or are, fixed to the vehicle. When the clamp mechanism is clamped the fixing rail and support brackets are fixed relative to one another. When unclamped the-shroud can move relative to the brackets to permit the required reach adjustment.
In the event of a crash it is desirable, and sometimes a legal requirement, for the steering column assembly to collapse in a controlled manner. This helps to reduce the forces of a driver colliding with the steering wheel or its airbag. A steering column which is arranged so that it has movable elements during an accident is known as a collapsible steering column assembly.
In one known arrangement the controlled collapse of a telescopically adjustable steering column assembly is enabled by connecting the first support bracket to the fixed part of the vehicle, and to the second support bracket, using one or more frangible connectors. The shroud is connected to the second support bracket by means of a clamp or fixed in the case of a non-adjustable column. In a crash the forces on the shroud are sufficiently high to cause the frangible connection to break, leaving the shroud and second bracket assembly, and hence an upper part of the steering column, free to move relative to the first support bracket.
To control the movement of the upper column during collapse, some form of energy absorbing device is typically provided that acts between the first support bracket and the vehicle body. The energy absorbing device in use absorbs energy in the event of a collapse of the steering assembly. In this context, a collapse is defined as movement of the shroud beyond its normal range of adjustment due to the application of force through the steering wheel along the axis of the steering column shaft. This will typically arise when the force from a driver's body passes-through the steering wheel in a crash. For a steering column assembly that is adjustable for reach the normal range of adjustment will correspond to the allowable reach adjustment of the steering and this should not be opposed by the energy absorbing device, since that would make the steering difficult to adjust for reach. The energy absorbing device controls the movement of the support bracket.